Spinal fixation system

ABSTRACT

A fastener assembly for a spinal fixation system that is particularly useful in treatment of pediatric and small-statured patients includes a fastener, an attachment member, and a locking member. The fastener has a lower portion for contacting a bone and an upper portion integral with the lower portion. The upper portion has two open channels. Each channel is configured and dimensioned to receive a portion of a longitudinal or connecting member along its circumference. The attachment member is positionable on the fastener and at least partially covers the channel that receives the longitudinal or connecting member. The locking member is operatively associated with the upper portion of the fastener and secures the attachment member and the longitudinal or connecting member to the fastener.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. application Ser. No.11/510,685, filed Aug. 25, 2006 now abandoned, which is a continuationof U.S. application Ser. No. 10/647,587, filed Aug. 26, 2003, now U.S.Pat. No. 7,118,571, which is a continuation of U.S. application Ser. No.09/915,572, filed Jul. 27, 2001, now U.S. Pat. No. 6,610,063, whichclaims the benefit under 35 U.S.C. §119(e) of U.S. ProvisionalApplication No. 60/221,518, filed Jul. 28, 2000. The entire contents ofeach are expressly incorporated herein by reference thereto.

FIELD OF THE INVENTION

The invention relates to a spinal fixation system, and in particular toa fastener assembly for securing a longitudinal support along a spinalcolumn.

BACKGROUND OF THE INVENTION

Stabilization of the spine is often required following trauma, tumor, ordegenerative pathologies. Each region of the spine presents uniqueclinical challenges as several vital neural and vascular structuresincluding the vertebral arteries, nerve roots, and spinal cord must beavoided during surgery. The anatomy of pediatric and small-staturedpatients presents additional challenges that makes assisting suchpatients even more difficult. For example, because these patients aresmall in stature, lower profile systems are required. Also, it may berequired to add fastener assemblies to an already assembled system,especially in pediatric patients. At the same time, it is desirous tokeep inventory at a minimum and have an assembly that requires as fewcomponents as possible.

Current methods of spinal fixation are not particularly well-suited forsmaller statured patients. U.S. Pat. No. 5,737,685 to Halm et al.discloses a bone screw that has a threaded shaft and a fork head. Thefork head has two legs which define a single groove that opens in thevertical direction for receiving a corrective pin. The upper end of thefork head has an outside thread and a head nut is screwed onto the outerthread. The head nut has inner threads which a fastening screw isscrewed to press onto the corrective pin. Because the groove opens in avertical direction it is difficult to add additional screws to analready installed fixation system.

U.S. Pat. No. 5,530,441 to Sherman et al. discloses an attachment plateconfigured for use with a spinal fixation element that has a posteriorlyprojecting central post. The attachment plate is generally L-shaped withan eyebolt engaging portion and a fixation element clamping portion. Thefixation element has grooves in the lateral surfaces of the central postand one lateral surface of the post contacts the spinal rod when the rodextends through an aperture of an eyebolt assembly. A flange extendsfrom the attachment plate and is configured to engage the oppositelateral surface of the post and the attachment plate includes a cammingsegment to provide a clamping force component directed toward the flangeto clamp the spinal rod to the fixation element post when a nut isthreaded onto the eyebolt threaded post. The attachment plate has a slotin the eyebolt engaging portion for receiving the posteriorly projectingthreaded post of the eyebolt body. Because the eyebolt must bepre-assembled onto the spinal rod, it is difficult to add additionalfixation elements to an already installed system.

U.S. Pat. No. 4,653,481 to Howland et al. discloses a spinal supportsystem that includes a plurality of screw clamp assemblies. Each screwclamp assembly has a threaded end for placement into the vertebra and asaddle assembly removably attached to the screw formed of upper andlower halves. Each of the upper and lower halves of the saddle assemblyare provided with at least one pair of mating grooves for accepting aspinal rod. All embodiments shown and described in the Howland '481patent have a two-part saddle assembly that is removable from the screwclamp shaft member.

In view of the foregoing, a need exists for an improved fixationapparatus for stabilizing the spine that can be assembled to an alreadyinstalled fixation system and that has minimal components.

SUMMARY OF THE INVENTION

The invention relates to a fastener assembly for a spinal fixationsystem. The fastener assembly includes a fastener, an attachment member,and a locking member. The fastener has a lower portion for contacting abone and a upper portion integral with the lower portion and having twoopen channels. Each channel is configured and dimensioned for receivinga portion of the longitudinal member along its circumference. Theattachment member is positionable on the fastener and at least partiallycovers the channel that receives the longitudinal member. The attachmentmember is configured and dimensioned for receiving another portion ofthe longitudinal member along its circumference. The locking member isoperatively associated with the upper portion of the fastener andsecures the attachment member and longitudinal member to the fastener.

The fastener can be a hook or a screw with the lower portion having athreaded end for engaging a vertebra. If the fastener is a hook, thehook can be provided with an arcuate portion and a flat portion forfacilitating implantation. The arcuate portion can have a dimple on aposterior surface to further facilitate implantation. In one embodiment,the locking member is a nut and the upper portion of the fastener has ashaft with external threads to accept the locking member.

The two channels of the fastener are preferably disposed on oppositesides of a central plane of the fastener with the two channels extendingorthogonally with respect to the fastener longitudinal axis andequidistant from the proximal end of the fastener. A bore can bepositioned transversely to the longitudinal axis and between the twochannels.

In an exemplary embodiment, the attachment member includes a cylinderhaving upper, lower, and side surfaces with a bore extending through theupper and lower surfaces and defining a longitudinal axis lying in acentral plane; a slot extending through the cylinder offset from thecentral plane and parallel with the central plane; and a protrusionextending from the bottom surface on an opposite side of the centralplane from the slot. The channels can define a seat for accepting theprotrusion of the attachment member. The slot can be provided withserrations along the inner surface. The slot can also have an eccentriccross-sectional shape with a geometry substantially conforming to adiameter of the longitudinal member.

The fastener can have a cavity extending longitudinally from the distalend for receiving a manipulation device. This manipulation deviceincludes a ball detent mechanism and a groove extending transversely tothe cavity and around its circumference for receiving the ball detentmechanism. Alternatively, the manipulation device has a threaded end andthe cavity of the fastener is cylindrical and includes threads along theinterior.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a fastener assembly accordingto the invention;

FIG. 2 is a side view of one embodiment of a fastener for the fastenerassembly of FIG. 1;

FIG. 3 is a front view of another embodiment of a fastener for thefastener assembly of FIG. 1;

FIG. 4 is a cross-sectional view of the upper portion of a fastener ofthe fastener assembly of FIG. 1 taken along a central plane;

FIG. 5 is a cross-sectional view of the attachment member of thefastener assembly of FIG. 1 taken along a central plane;

FIG. 6 is a cross-sectional view of another embodiment of the attachmentmember of the fastener assembly of FIG. 1 taken along a central plane;

FIG. 7 is a bottom view of the attachment member of FIG. 5;

FIG. 8 is a side view of the fastener assembly of FIG. 1 showing thefastener as a hook;

FIG. 9 is a front view of one embodiment of a manipulation deviceaccording to the invention;

FIG. 10 is a front view of another embodiment of a manipulation deviceaccording to the invention;

FIG. 11 is a cross-sectional view of the fastener of FIG. 2 taken alonga central plane;

FIG. 12 is a back view of the fastener of FIG. 2; and

FIG. 13 is a perspective view of a transverse bar according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the fastener assembly 10 according to the inventiongenerally includes a fastener 12, an attachment member 14 positionableon fastener 12 and a locking member 16 securable upon fastener 12. Thefastener assembly 10 may be used in a spinal fixation system to secure alongitudinal member 18, such as a rod, along a spinal column. Fastener12 has a lower portion 20 for engaging a vertebra, and an upper portion22 integral with lower portion 20 for securing the longitudinal member18 to fastener 12.

Referring to FIGS. 2 and 3, lower portion 20 of fastener 12 preferablycomprises a hook or pedicle screw, and has a longitudinal central axis24 extending from a proximal end 25 to a distal end 27 and lying in acentral plane. In FIG. 2, lower portion 20 comprises a hook 28 andincludes a curved hook body 29 with a first end 30 connected to theupper portion 22 and a second free end 31. Hook body 29 is convex on itsposterior side 32. Free end 31 runs essentially perpendicular to thecentral axis 24 and is adapted to the spinal geometry. As can be seen inFIG. 3, in another embodiment, lower portion 20 comprises a pediclescrew 80. Pedicle screw 80 comprises a screw body 82 with a screw point84 and a thread 86 on the outside of the screw body 82 for engaging thevertebra. Preferably, the screw 80 is self-tapping and includes a bluntscrew point 84.

Referring to FIGS. 1-4, the upper portion 22 is generally in the form ofa shaft 26 extending along central axis 24 and accepts the attachmentmember 14 and the locking member 16. Upper portion 22 has a shoulder 33at a first end adjacent the lower portion 20 and an external threadedportion 34 at the distal end 27 of fastener 12. At least two channels 35traverse the shaft 26, and the channels 35 are preferably disposed onopposite sides of the central plane. The channels 35 extend orthogonalwith respect to the central axis 24 and are preferably equidistant fromthe distal end 27. Preferably a bore 36 runs between the channels 35transverse to the central axis 24 to facilitate the machining of acavity 37 in the distal end 27 of fastener 12. The external threading 34engages internal threading of locking member 16 so that locking member16 is tightenable on the shaft 26.

Each channel 35 is configured and dimensioned for receiving at least aportion of the longitudinal member 18. In a preferred embodiment,longitudinal member 18 is an elongate rigid rod having a circularcross-section taken in a plane extending perpendicular to thelongitudinal central axis of the rod. As best seen in FIG. 4, inaccordance with this embodiment, channels 35 preferably have an arcuatesection 40 centrally disposed between upper 42 and lower 44 legs openingsubstantially laterally with respect to the central axis 24 of shaft 26.Arcuate section 40 has a diameter substantially conforming to thediameter of the rod. Preferably, the lower leg 44 extends furtherradially outward from the central axis 24 than upper leg 42 and definesa seat 46 for supporting a portion of the attachment member 14. Numerousother embodiments are envisioned in which the longitudinal member mayhave varied cross-sections, such as a rectangular bar or ellipticalwire. Accordingly, channels 35 can have numerous shapes corresponding tothe particular geometry of the longitudinal member used.

Referring again to FIG. 1, the attachment member 14 preferably has agenerally cylindrical shape having upper 48, lower 50 and side 52surfaces with a bore 54 extending through the upper 48 and lower 50surfaces along central axis 24. Bore 54 extends through the attachmentmember 14 so that the attachment member 14 can be inserted over theexternal threading 34 to be positionable on the upper portion 22 offastener 12. A slot 56 extends transversely through the attachmentmember 14 and is orthogonal to central axis 24 and offset from thecentral axis 24. Slot 56 is configured and dimensioned for receiving thelongitudinal member 18 and locatable adjacent either of the channels 35for securing the longitudinal member 18 to the upper portion 22 offastener 12. When the longitudinal member 18 is inserted in channel 35and attachment member 14 is assembled upon the upper portion 22, lockingmember 16 tightens attachment member 14 to secure the longitudinalmember 18 in slot 56 and against one of the channels 35.

Locking member 16 substantially resembles a nut and has a generallydisc-like shape with top 60, bottom 61 and side 62 surfaces with a hole63 extending centrally through the top 60 and bottom 61 surfaces. Thehole 63 is provided with internal threading 64 which mates with externalthreading 34 provided on shaft 26 of upper portion 22. As such, lockingmember 16 is tightenable on the shaft 26 and the bottom surface 61contacts the upper surface 48 of the attachment member 14 to force theattachment member 14 downward toward the lower portion 20 as lockingmember 16 is tightened. Side surface 62 is preferably provided with apolygonal geometric configuration comprising twelve points to facilitatetightening.

The slot 56 has a generally cylindrical cross-section and has a geometrysubstantially conforming to the diameter of the longitudinal member 18.Preferably, slot 56 has an eccentrically shaped cross-section. Referringto FIG. 5, slot 56 comprises multiple circular sections having centersoffset with respect to one another to define an inner surface 57 towardsthe central axis 24 connecting inner section 53 with outer section 55.Inner and outer sections 53, 55 preferably have circular geometries.Inner section 53 has a center of curvature C_(i) offset inward towardscentral axis 24 with respect to a center of curvature C_(o) of outersection 55. The eccentric shape of inner surface 57 is useful to allowthe camming of longitudinal member 18 towards the channels 35 when theattachment member 14 is tightened onto upper portion 22 as inner section53 allows for movement of the longitudinal member axially inward toforcibly engaging the longitudinal member 18 with either of the channels35. As can be seen in FIG. 6, in one embodiment of attachment member 14,the slot 56 includes serrations 62 along inner surface 57 for engagingcorresponding ridges 65 on a ridged longitudinal member, such astransverse bar 66 (FIG. 13). In this way, the ridged longitudinal memberis less likely to rotate relative to fastener 12 when the attachmentmember 14 is secured by locking member 16.

Referring to FIGS. 5-7, a protrusion 68 extends from lower surface 50 onan opposite side of the attachment member 14 from slot 56. Protrusion 68preferably extends generally perpendicular from lower surface 50 and isspaced radially inward from the side surface 52. Also preferably,protrusion 68 runs arcuately along a portion of lower surface 50opposite slot 56. As such, when attachment member 14 is assembled uponthe upper portion 22 of fastener 12, the protrusion 68 preferablyengages seat 46 for preventing the attachment member 14 from tiltingwhen the attachment member 14 is tightened by locking member 16.

As shown in FIG. 8, upper portion 22 of fastener assembly 10 has aheight H measured from the base of shoulder 33 to the top surface 60 oflocking member 16. Preferably height H is as minimal as possible andonly slightly greater than the diameter of longitudinal member 18.Preferably height H is less than 10.0 mm. Also, preferably the ratio oflongitudinal member diameter D to height H is greater than 0.50 so thatthe upper portion 22 has only a slightly higher profile than thelongitudinal member 18. A notable advantage of maintaining such a lowheight H, or low profile, is that such a fastener assembly 10 isespecially well suited for use in pediatric and small-statured patients.

Referring again to FIG. 4, fastener 12 consists of a cavity 37 in distalend 27 opening upward and having a hexagon socket 38 near the distal endand a cylindrical hole 39 running in the direction of longitudinalcentral axis 24, for receiving a manipulation device 70 (FIG. 9) tofacilitate the insertion of the fastener 12 into bone. Cylindrical hole39 is preferably provided with internal threading that continues fromthe base of hexagon socket 38 in the direction of lower portion 20 forthe positive acceptance of manipulation device 70 with correspondingexternal threading 71 (FIG. 9). Here, cavity 37 permits arotationally-stable, releasable connection with manipulation device 70.Internal threading can be designed with multiple threads to stronglyshorten the time required for the connection process. For thisembodiment, manipulation device 70, shown in FIG. 9, consists of hollowcylindrical sheath 73 that has at its one end 74 lug 75. From the otherend 76 of sheath 73, a cylindrical pin 77 can be inserted into sheath73. Cylindrical pin 77 carries at its one end external threading 71that, after successful insertion, protrudes beyond end 74 of sheath 73,and at its other end, grip 78 protrudes from sheath 73 and serves totighten the connection.

Preferably a generally rectangular groove 72 extends transverse to thehexagon socket 38 and around the circumference of the cavity 37. Asshown in FIG. 10, another embodiment of the manipulation device 70 isprovided with bearings 79 in lug 75 for engaging groove 72. Whenmanipulation device 70 is introduced into cavity 37 and bearings 79align with rectangular groove 72, pin 77 can be pushed through thesheath 73 in manipulation device 70 to press bearings 79 intorectangular groove 72. This facilitates the transfer of tensile,compressive and rotational forces via manipulation device 70 without theneed to have a threaded coupling.

Referring to FIG. 11, at convex posterior side 32 of hook body 29 adimple 100 is provided to accept an installation device (not shown).Dimple 100 comprises a cylindrical hole extending along a longitudinalaxis 101 at an angle with respect to the central axis 24. Referring toFIG. 12, preferably dimple 100 is located centrally with respect to theposterior side 32. In this way, dimple 100 provides an ideally suitedstructure for impaction to facilitate the insertion of flat end 31 intothe vertebra.

Referring to FIG. 13, a transverse bar 66 is shown which may be used asa connector or connecting member to secure the longitudinal member 18 toa fastener 12 that is laterally displaced from member 18 to avoidexcessively bending member 18. The transverse bar 66 includes a hook 130at one end 132. A set screw 134 extends through the hook 130 and pinsthe longitudinal member 18 against the inner surface 136 of the hook 130to secure the longitudinal member 18 to the transverse bar 66. Thesecond end 138 of the transverse bar 66 is a shaft that has ridges 65around the circumference that mate with serrations 59 provided inattachment member 14 as described above.

In use, a plurality of fastener assemblies 10 are inserted into thevertebra along the spine with the aid of the manipulation device 70 andthe longitudinal member 18 is placed in one of the two channels 35 oneach of the fasteners 12. An attachment member 14 is placed onto each ofthe fasteners 12 so that the longitudinal member 18 is held in thechannel 35 by the slot 56 of attachment member 14. A locking member 16is then used to secure the longitudinal member 18 in the channel 35.Also, a transverse bar 66 can be secured to the longitudinal member 18to couple the longitudinal member 18 to a laterally positioned fastener12. In that case, the hooked end 132 of the transverse bar 66 is held tothe longitudinal member 18 by a set screw 134 and the opposite end 138of the transverse bar 66 is secured to the fastener 12 by an attachmentmember 14 in the same fashion as described above for the longitudinalmember 18.

Because of the dual-channel structure of the fastener 12, a surgeonimplementing a spinal fixation system may insert the longitudinal member18 in either channel 35. Also, because the slot 56 is offset withrespect to central axis 24, the attachment member 14 may be located oneither side of fastener 12 and the longitudinal member 18 may be securedto either one of channels 35. As a result, fastener assembly 10 may beassembled on either side of the spinal column using the identicalcomponents. Further, the integral nature of the upper and lower portions22, 20 allows for easy assembly to an already installed spinal fixationsystem. Because the channels 35 open laterally fastener 12 can beanchored to a vertebra and longitudinal member 18 may be laterallyreceived in upper portion 22 and attachment member 14 can be verticallyassembled there over to secure the longitudinal member in place, and nopreassembly is required.

While it is apparent that the illustrative embodiments of the inventionherein disclosed fulfill the objectives stated above, it will beappreciated that numerous modifications and other embodiments may bedevised by those skilled in the art. Therefore, it will be understoodthat the appended claims are intended to cover all such modificationsand embodiments which come within the spirit and scope of the invention.

1. A fastener assembly for a spinal fixation system, the spinal fixationsystem including a longitudinal member that is positionable along aspinal column, the fastener assembly comprising: a fastener including acentral axis, a proximal end, a distal end, a lower portion configuredto contact a bone, and an upper portion having first and second upperlegs, first and second lower legs, a first channel defined by the firstupper leg and the first lower leg, and a second channel defined by thesecond upper leg and the second lower leg, the first and second channelsbeing disposed on opposite sides of the central axis, wherein the firstand second lower legs extend further radially outward with respect tothe central axis than the first and second upper legs such that thefirst and second lower legs define first and second seats respectively;and an attachment member positionable on the fastener such that theattachment member at least partially covers the first channel, theattachment member including a slot and a protrusion on an opposite sideof the central axis from the slot, wherein the first channel and theslot are each configured to retain a portion of the longitudinal memberwhen the attachment member is positioned on the fastener, and theprotrusion is configured to engage the second seat when the attachmentmember is positioned on the fastener.
 2. The fastener assembly of claim1, wherein the upper portion is integral with the lower portion.
 3. Thefastener assembly of claim 1, further comprising: a locking memberincluding internal threading, the internal threading engaged withexternal threading of the upper portion in the assembled configuration.4. The fastener assembly of claim 1, wherein the first and secondchannels extend orthogonally with respect to the central axis and areequidistant from the proximal end of the fastener.
 5. The fastenerassembly of claim 1, wherein the upper portion has a bore positionedtransversely to the central axis, the bore located between the first andsecond channels.
 6. The fastener assembly of claim 1, wherein the slotincludes serrations along an inner surface.
 7. The fastener assembly ofclaim 1, wherein the slot has an eccentric cross-sectional shape.
 8. Thefastener assembly of claim 1, wherein the slot has a generallycylindrical cross-section with a geometry substantially conforming to acircumference of the longitudinal member.
 9. The fastener assembly ofclaim 1, wherein the lower portion comprises a thread for engaging avertebra.
 10. The fastener assembly of claim 1, wherein the upperportion includes a cavity extending longitudinally from the distal end.11. The fastener assembly of claim 10, wherein the cavity is cylindricaland includes threads along the interior.
 12. The fastener assembly ofclaim 1, further comprising: a locking member having internal threads,the upper portion includes a shaft having external threads forthreadably engaging the internal threads.
 13. The fastener assembly ofclaim 1, wherein the lower portion comprises a hook and includes anarcuate portion and a flat portion.
 14. The fastener assembly of claim13, wherein the arcuate portion has a dimple on a posterior surface.